The invention relates to a control valve for viscous materials such as concrete mixes. The present valves are equally adapted for cooperation with single cylinder piston pumps as well as with double cylinder piston pumps for conveying concrete mixes. Such valves control the supply of concrete mix into a pump cylinder as well as the discharge of the concrete mix from the pump cylinder into a conveyor conduit connected to the pressure outlet port of the pump. Such valves may be equipped with valve plates which are shiftable back and forth by means of push rods in order to open or close a respective port when the plate or plates are in their end positions. Such valves are also equipped with the drive means for shifting the valve plates back and forth, including support means and rinsing or scavenging means as well as sealing means in a valve housing. The filling funnel is arranged above the suction channel.
Prior art modifications of the just described slide valves include tilting pipe slides, gate slides, roller slides, plate slides or combinations of the just mentioned systems.
German Utility Model No. 6,904,407 describes a plate slide or rather, plate slides for controlling the feed advance sequence in a so-called slush pump. Such pumps are capable of transporting highly viscous materials and the plate slides constitute the control slides as part of such a pump. The plate slides of the known control valve, according to said German Utility Model No. 6,904,407 are driven by hydraulic piston cylinder drives, whereby each plate slide controls either two suction ports or two pressure ports. The slide plate which controls the suction port is arranged horizontally below the filling funnel, whereby it closes the respective suction opening on the side of the pump on which the piston performs the pressure stroke. As a result of this arrangement a space is provided at the highest point in the pressure channel which space is not utilized because the medium to be conveyed does not flow through this space during the pressure stroke. Please also see in this context German Patent Publication (DAS) No. 1,678,445.
The material to be conveyed flows past and below this so-called dead space, whereby air accumulates in the dead space since such air is always contained in the concrete mix. The suction inlet opening is arranged adjacent to the plate slide and the latter does not close the suction inlet opening so that the material may flow from the filling funnel through said opening into the cylinder in which the piston of the pump performs the suction stroke. The piston on its suction stroke evacuates the pump cylinder as the piston moves back, whereby the concrete mix is filled into the evacuated cylinder under the influence of the atmospheric pressure to which the filling container is exposed. During this operation air flows from the dead space of the pressure side into the suction channel because the control slide or valve of these pumps is not airtight. Such airflow has the disadvantage that the suction cylinders are only incompletely filled with concrete mix.
In view of the above, prior art concrete pumps of the just described type have consistently a poor cylinder filling factor, especially where it is desired to transport the concrete mix with a large densification factor because the air bubbling out of the concrete mix on the pressure side is returned into the concrete mix on the suction side of the pump.
According to another prior art control valve for concrete mix pumps, a suction channel and a pressure channel are opened and closed in alternating succession by means of a plate slide. The plate slide of this prior art control valve is arranged between the two push rods extending in parallel to each other. The guiding of this type of push rods requires four bearings which depend on each other with regard to their adjustment. Arranging these bearings in exact axial alignment is rather difficult which means that this type of plate slide has a tendency for jamming, especially when the valve must operate under a relatively high pressure. Due to the just mentioned difficulties which have been encountered with flat, plate valve slides actuated by two push rods, concrete pumps are presently not equipped with such slide control valves.
The above mentioned control valves for concrete pumps are driven by hydraulic piston cylinder means, the housing of which is rigidly connected to a support structure and the piston rod of which is operatively connected to the push rod of the slide plate. The piston diameters of the hydraulic piston cylinder means is larger than the diameters of the push rods. Thus, a spacing is provided between the inner cylinder walls and the push rods and this spacing receives a rinsing or scavenging liquid which is taken out of a rinsing or scavenging liquid container by the suction movement of the piston and returned into the rinsing or scavenging liquid container with the pressure stroke of the piston. In operation of these prior art devices, the piston surface of the piston cylinder drive facing the push rod is subjected to a pressure medium. However, the sealing means provided between the concrete and the liquid cannot always completely prevent that components of the concrete mix such as fine sand and cement enter into the rinsing liquid.
Another problem with the described prior art devices is seen in that it is not possible to achieve an absolute sealing between the rinsing liquid and the pressure medium. In other words, the piston cannot be so completely sealed in the piston cylinder arrangement to achieve such a separation between the rinsing liquid and the pressure medium. Thus, components of the concrete mix not only enter into the rinsing liquid, but also into the pressure medium, whereby fine sand particles and cement enter into the hydraulic circuit which results in heavy damage to the hydraulic main pump which may even become completely unrepairable and thus useless. Thus, in order to prevent the entrance of solid particles from the concrete mix into the rinsing or scavenging liquid, it is necessary to frequently exchange the sealings of the control slides. Such exchanging becomes even more frequent as wear and tear progresses.
In the prior art devices the sealing means are located on the push rods behind or in front of the drive piston cylinder means. In addition, the sealing means are fixed in the housing of the control valve. Thus, in the prior art valves the sealings can only be exchanged by disassembling the piston cylinder drive means. This has the disadvantage that due to the substantial man hours required for the exchange of the sealings and the resulting costs, the sealings are rarely exchanged at the time when they should have been exchanged, namely, well before they reach a state in which they are completely useless. Neglecting the exchange of the sealing has happened, although the costs for removing the resulting damages, namely, replacing the entire pump, are generally substantially higher than the costs for the replacement of the sealings.